Nonlinear optical dyes (organic molecules having large nonlinear polarizabilities) have been recognized as potentially useful as components of the optical elements in optical frequency converters and in electrooptic devices. Generally, in order for the NLO dyes to exhibit the large second order optical susceptibilities essential to nonlinear optic applications, the molecules must be constructively arrayed in a noncentrosymmetric configuration. Such molecules have been crystallized in a noncentrosymmetric space group, but this method does not work for all potentially useful molecules, and the resulting shape and properties are limited by the very nature of a crystal.
The NLO dyes have been used, for example, in combination with glassy polymers to provide nonlinear optical elements. The choice of the dye molecule and glassy polymer affects the stability of nonlinear optical effect obtained, because the dye molecules have a tendency to "relax" over time, thereby losing the configuration necessary for the enhanced nonlinear optical properties.
The use of certain amorphous thermoplastics as hosts for NLO dyes in nonlinear optical elements is known, see for example H. L. Hampsch, et al., Polym. Commun., vol. 30, p. 40-43 (1989).
The electrical properties and chemical stability of a glassy polymer used in optical elements are important, since these characteristics are relevant to the efficient functioning of devices in which the nonlinear optical elements are generally employed. Thus, when choosing a host polymer for NLO dyes, pertinent properties for consideration include low water absorption, thermal and chemical stability, dielectric constant, and thermal coefficient of expansion. Polyimides are often used in electronics applications since many of their properties makes them especially suited for such uses.
S. Ermer, et al., Polym. Prepr., vol. 32, p. 92-93 (1991) and J. W. Wu, et al., Appl. Phys. Lett., vol. 58, p. 225-227 (1991) dissolved NLO dyes in polyamic acid precursors to polyimides, and while heating the mixture to high temperatures to form the final polyimide polymer, poled it in an electric field to align the dye molecules. The polyimides produced in these publications are not processible (i.e., they are insoluble and/or decompose before melting). Moreover, the high temperatures employed in converting the polyamic acid to the polyimide, are considered conducive to significant undesirable sublimation and/or chemical decomposition of the dye molecules.